Fails with 'width must allow for borders'

[SButterfly]

    @Override
    public String toString() {
        AsciiTable at = new AsciiTable();
        at.addRule();
        at.addRow(getHeaders());
        int lastLine = getLastLine();
        for (int i = 1; i <= lastLine; i++) {
            at.addRule();
            at.addRow(getValuesList(i));
        }
        at.addRule();

        return at.render();
    }

Stacktrace:

0 = {StackTraceElement@6467} "de.vandermeer.asciitable.CWC_AbsoluteEven.calculateColumnWidths(CWC_AbsoluteEven.java:45)"
1 = {StackTraceElement@6468} "de.vandermeer.asciitable.AT_Renderer.renderAsCollection(AT_Renderer.java:167)"
2 = {StackTraceElement@6469} "de.vandermeer.asciitable.AT_Renderer.render(AT_Renderer.java:128)"
3 = {StackTraceElement@6470} "de.vandermeer.asciitable.AT_Renderer.render(AT_Renderer.java:112)"
4 = {StackTraceElement@6471} "de.vandermeer.asciitable.AsciiTable.render(AsciiTable.java:185)"

What I did wrong ?